Visual-Feedback Distortion in a Robotic Rehabilitation Environment

We create a robotic rehabilitation environment that distorts the visual feedback of a movement representation to restore lost movements. The use of visual-feedback distortion produces a perceptual gap between the perceived (visual) and actual somatosensory experiences, in which movements can be manipulated without patients´ knowledge. Previously, we reported the smallest amount of distortion that is imperceptible by measuring just noticeable difference (JND), the distortion size that is tolerable without detection, and the invariance of perceived physical effort under visual-feedback distortion. In this paper, we report the performance changes under visual-feedback distortion in a robotic rehabilitation environment. By interleaving trials with no visual feedback, we showed that the internal somatosensory representation of the movement goal changed along with visual distortion for unimpaired and motor-impaired subjects. In addition, a gradual change of visual-feedback distortion within one experiment allowed movement changes significantly larger than the JND. These changes were robust under sudden lack of visual feedback and even when subjects were informed of possible distortion ahead of time. Finally, preliminary results of a six-week rehabilitation paradigm are reported. Improvements in the patient´s hand condition were found, particularly in the range of motion of the index and middle fingers